Occupational exposure to asbestos has long been recognized as being associated with adverse health effects, more recently the likelihood of exposure of the population at large to ambient concentrations of asbestos has been recognized. The conventional methods of measuring asbestos have a number of limitations associated with them that prevent their use for inexpensive instanta neous and continuous monitoring of asbestos concentrations in or near asbestos sources. The objective of this study is to develop and test a continuous monitor for the identificatin and counting of asbestos fibers in the ambient air, and in the occpation and residential environment. The instrument determines the size and asymmetry of a dilute suspension of particles large compared with the wavelength of incident polarized light by measuring the scattering, birefringence or dichroism of the particle as it is aligned, through an external moderate-sized electric field, first parallel to and then perpendicular to the incident polarized light.